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Tuesday, September 30, 2008

So, in thinking about Xyloplax, I was wondering WHAT is it exactly that seems to attract people to the really oddball animals.

I touched on some of the weirdness in the first Xyloplax post..but here are a few other aspects of the "Xyloplax Phenomenon" that is common to so many weird animals in the field...1. RarityPeople are fascinated by the rare and rarely encountered. Xyloplax has 3 species-all found from distant locales at great depth. Until the one discovered in 2004, there was a 17 year gap until it was found again!!!

So, they ain't too common...Here's the breakdown:

Xyloplax medusiformis. Described in 1986 based on less then a dozen specimens from New Zealand. AND found while people were looking for OTHER wood-living deep-sea critters...

Xyloplax turneri. Described in 1987 based on over a 100 specimens, but oddly, collected in 1980 from the tropical Atlantic!!! Collected FIRST by Dr. Ruth Turner at the MCZ and then later published as the second Xyloplax species by Frank Rowe.

2. Mystery
One of the other weird things..here is an animal that we have invested an enormous amount of energy in studying..but what do we ACTUALLY know about its biology? its ecology? What it eats in the morning? DOES it eat anything in the morning??There have never been any REAL published observed of this animal alive or even in situ!! What does it DO with those spines? Why doesn't it have a well-developed gut?

Some useful information was inferred from the tissue analysis (reproduction, etc.) but ultimately we know little about its life habits.

Xyloplax is like a wonderous, wonderous piece of mystery dessert..we don't know what's IN it..but we want to taste it because it seems to be SO tantilizing on the OUTSIDE....

3. History
Okay...so this is the big one and related to the MYSTERY. How do you GET such an extreme morphology? How does EVOLUTION get you from a starfish to whatever-the heck Xyloplax is??? the problems/challenges that have followed this issue are big ones, and hence the appeal...including:

Homologies. What are the corresponding structures that have been modified over time? We can see forelimbs in fish and monkeys pretty easily but for echinoderms? Much more difficult. Several papers have argued and even redefined basic concepts of homology within Xyloplax.

Morphology is Highly Derived. All the structures are SO far beyond what we see in other echinoderms..its hard to say exactly what kind of evolutionary "signal" gets through. What is an adaptation? What is an ancestral trait?

Some notions and a brief review of some early and major ideas:

A. Non-Asteroid (i.e. Starfish) Relationships. On one hand, there was serious consideration of Xyloplax's relationship within the Echinodermata. Is it a highly modified ophiuroid? a weird sea urchin?? a crazy modified sea cucumber?? REALLY a separate class all on its own???

One early but idea proposed that Xyloplax was possibly related to the Paleozoic Cyclocystoidea??Cyclocystoids were a weird group of disk-shaped echinoderms that lived in the Paleozoic and look kinda like cookies with a series of plates in a solid ring around the edge. Little is known about them other than that their appearance as being "medusoid" in shape with a structural ring around the edge and a bunch of plates in the center.

Eventually the overall morphology was interpreted as dissimilar to Xyloplax..which was thought to be more closely related to asteroids...(aka starfish, sea stars) but really..the question was open for awhile.

but the Million (Sand) Dollar question over the years....???B. Asteroid-Related Relationships-WAS Xyloplax a separate class/lineage??This was the original historical proposed idea from 1986. Based primarily on the radically different morphology..it was a stand-alone group. Originally, a class on par with the other "Big 5" but argued as related to asteroids.

A formidible amount of morphological data was provided: histology, morphology, sperm morphology. This perspective ultimately argued for a separation of Xyloplax based on its distinctive character suite.

With the advent of phylogenetics/cladistics-which argued for characters that are SHARED rather than characters that separate, even the paradigm of how to look at Xyloplax had changed. ...OR Was Xyloplax ACTUALLY a starfish??? (i.e., included as a member of the Asteroidea)

Xyloplax is an early divergence away from this "mainstream" group (so in theory...it can be an asteroid but is NOT a starfish-think of it as a relict or a failed experiment from the early explosive diversification of early asteroid body plans).

So what?
From here what's left?

We still don't have a complete phylogeny of the Asteroidea on which to hang our inevitable, next Xyloplax data... (although I am working to remedy this issue..)

Will the basal split that I saw from morphology also be reflected in molecular data?

Sunday, September 28, 2008

This week, I thought it would be fun to discuss one of the weirdest of the weird-the beasts that we consider odd EVEN for the weirdest phylum of animals: The Echinoderms!!....What beast dares to contend for this title???
Starro??? The Star Conqueror??? (well..it would be cool if...) sadly..no!!Its The legendary Sea Daisy-Xyloplax (Concentricycloidea)!!
In 1986, 3 of world's most prominent echinoderm biologists, Alan Baker and Helen Clark from the National Museum of New Zealand and Frank Rowe from the Australian Museum in Sydney described a NEW beast that was truly stunning that it was published in Nature!!This new beast was placed into a new CLASS of living echinoderms! The first to be described since 1821!!
Thus, it had parity with the other living "Big 5"..the Asteroidea, the Ophiuroidea, the Holothuroidea, the Echinoidea, and the Crinoidea. But why? What made it so distinctive? So interesting?? It was clearly an echinoderm but there were so many STRANGE things about it which were captivating!

but perhaps most stunningly unsual? its body form...similar to other echinoderms-it had the calcium carbonate skeleton, the tube feet, and the pentameral symmetry that one saw in other echinoderms..
But its body form held MANY strange and radical skeletal differences not observed in OTHER known echinoderms:

The radial water canals were arranged into concentric (i.e., one inside the other) rings (Note that It was here that the Class name "Concentricycloidea" was derived. From "concentric" alluding to the skeletal rings..and "cycloidea" for round body (or something thereabouts).

Along those lines..the tube feet were arrayed in a RING and not in the usual paired or linear arrays seen in other living echinoderms

The gut was nearly gone or absent.

Its whole body was basically one big umbrella of plates, spines and some tissue holding it together....

There was a ring of spines around the edge.

Xyloplax intrigues us BECAUSE of this extreme body weirdness. The morphological features are SO strange and warped and extreme that it has made the search for understanding the evolution and relationships a huge quest in its own right!!
And that is where I will pick up later this week with Xyloplax pt. 2: Conundrums & Controversies!

Monday, September 22, 2008

By now, most everyone has heard that great story (possibly apocryphyal) of that guy who went rooting through his grandfather's or his father's old stuff in the attic and while riffling through a box that hadn't seen the light of day in 40 years-discovers a copy of the oh-so-rare and VALUABLE comic book-Action Comics #1 (first appearance of Superman)!!!!

Natural history museums have their "Action Comics #1" stories as well!! Our story begins over 30 years ago or so with famous echinoderm biologist H.B. "Barry" Fell (an awesome bio is here.) who for various reasons shifted his research from echinoderm systematics to Maori languages in the early 70s.

As a consequence, many of the echinoderm specimens in his care were inherited by a PhD student, who got his degree but ultimately had to leave systematics-as the 70s-80s were not a great time, jobwise, to be an echinoderm biologist and so the student did what he could: he placed the specimens into deep-storage.
The student continued his research where he could-but ultimately was motivated to deposit/return the collection to Barry Fell's most prominent student in North America-David Pawson, curator of Echinodermata at the Smithsonian. That student returned over 500 lots of ophiuroids, starfish, crinoids, and sea urchins which had been "out of circulation" for over 30 years!

After these boxes arrived, I began pecking through them to check for proper identifications and to begin specimen curation, so that specimens which looked like thisCould be re-housed and stored in snazzy, clean and protective archival plastic bags or boxes like this one:
Along the way, I found a bunch of echinoderms stored in these AWESOME antique style boxes:But what was REALLY amazing? Discovering specimens that had these tags:It turns out that these (and several other lots) were LOST type specimens!!! What are type specimens??? Type specimens are the original specimens on which the description of any species is based. The type specimens are those which are used to describe a new species in the original manuscript.
Typically, these specimens are housed in museums under lock and key. It is these specimens that the "identity" of any given species is tied to (unless the species is particularly well-known).

Concepts of economically important or otherwise ecologically important species can be tied up based on the concepts expressed by these specimens.
One can draw an immediate parallel with Action Comics #1.
Think of type specimens as the early issues of a superhero appearance!!
The "first issue" is the first relevant appearance of that species:

*It sets up the look (i.e., the morphological or physical description)

*The story (i.e., what the author intended for the species to look like)

*And sets up other accessory characters or story elements (i.e., other related species, comparisons, etc.).

Sadly, (or perhaps fortunately) type specimens seldom if ever carry an actual cash value.
But they are VITAL parts of the taxonomic museum landscape because fundamentally, you can't do anthing in systematics or ecology without the foundation established by these specimens.

Nothing feels better than a good afternoon going through a box of dusty old specimens, going through some history...and discovering some...great historical treasure right in your hands! Action Comics #1? Or paratypes for Pseudechinaster rubens?? Either way....a good day.

Wednesday, September 17, 2008

What I didn't know was that there are actually GRADES of uni available. The CSUC describes them as such:

The Commission also adopted the following grade names and standards of quality to encourage uniformity throughout the industry, to help retail and consumer customers make better purchasing decisions, and to give assurance of product quality.

“Premium California” - gold, yellow or orange color but less brilliant than California Gold; firm buttery texture; salty ocean scent; with a crisp and nutty taste. Uni sections are smaller but still primarily intact pieces. Premium uni is used for sushi, soups, salads, or combination dishes where uni is the featured item. (formerly grade B)

“Select California” - medium hues of yellow and orange or even tending to brown in color; salty ocean scent; softer creamy texture; with a more neutral nutty taste. Uni may be intact sections but can consist of broken pieces of the other grades. Frequently Select is packaged and shipped frozen. Uses include soups, sauces and dishes where the uni is mixed with other ingredients, including other seafood. (formerly grade C)

Monday, September 15, 2008

If you've ever enjoyed the fine diversity of Japanese cuisine, and are a serious sushi connaisseur (as I am) you have probably experienced the singular love of uni-a type of sushi made from the gonads (which produces the roe) of a sea urchin. To be sure, uni is not something everyone "gets" the first time they try sushi.But, for people who enjoy uni, they REALLY enjoy it. Its a compulsion to order it when they visit the sushi bar!! But why???

That being said can sea urchins handle the fishing stress?Incidentally, according to one of the papers I found, the chemical in S. purpuratus can reduce the fertilization capacity of sperm cells. This study was via direct application-not via ingestion, but if you are trying to be fertile, it probably doesn't hurt to lay off the uni, if you're having it every night! (plus uni is quite rich..so you probably can have too much of a good thing!!).

Tuesday, September 9, 2008

So, the other day, was looking through one of my favorite older monographs "On Some Remarkable Forms of Animal Life...Researches on the Structure and Affinity of the Genus Brisinga" by George Ossian Sars, Professor of Zoology at the University of Christiania and came upon this cool older idea of Echinoderm Phylogeny:
The phylogeny recounts some very early and....unusual...ideas about metazoan relationships originally developed by Ernst Haeckel and modified by Sars. The monograph was published in 1875. Darwin's ideas on evolution had only been around since 1859.

This particular monograph emphasized brisingids, which look sorta like a cross between a "normal" looking starfish and a brittle star:
but what was NEAT and weird about Sars take on this animal's history?
The fundamentals of this phylogenetic idea was that the Echinodermata were formed by "Colony Forming Vermes" which was another way of saying "Let's take 5 of these"
and turn them into something kinda like this:
But Sars hypothesized that brisingids were essentially a separate and independent "step" between these "colony forming vermes" and starfish and other echinoderms...essentially a missing link to ALL echinoderm diversification!!
And that seems kinda reasonable (in a naive way)..when you look at it...

I could easily see how this could be "spun" this into the ancestor of crinoids, ophiuroids, and asteroids+echinoids+holothuroids!

The general gist of the phylogeny from there is that echinoderms were given towards greater "concrescense" or centralization...So from independent worms coalescing to bigger, lumpier things. So holothurians or sea cucumbers would be chief evidence of "concrescence"..especially with something like the armored and essentially sessile Psolus, which was seemingly even LESS pentameral than other cucumbers.

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
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